J. Freed

Today I collected 2 phase noises, first phase noise is of the 80 MHz OCXO after it has gone through an RF distributer. The reference was the SRS SG382 at 80MHz

The second is of the Double Mixer again but with an extra focus on the 8192Hz sideband.The reference was agian the SRS SG382 at 80MHz-4096Hz

These tests was done with the direct plug in method without using a PLL. This requires both the device under test and the reference device to be at quadrature. Normally a PLL is required to keep them there, however since both devices are connected to the LIGO timing system in some way,  a PLL is unnecessary to keep them locked in quadrature. To put them in quadrature I just lined them up on an oscilloscope best I could then added 90 deg by adjusting the phase on the SRS.  I bypassed the internal amp of the BluePhase1000 for all tests.

DM_vs_RF.pdf Is a plot of the two phase noises, as seen, the low frequency noise (<2Hz) has these humps. I now attribute these to the RF distributer causeing a shape change in the pure sin wave signal. 

RF_Distributer_Signal.jpg Shows how the RF distributer has a not exact sin wave (Yellow) compared to the SRS Pure tone (Blue)

DM8kSideband.pdf Shows a close up on the 8k sideband that will also couple into our SPI output